Bonding & Naming & Formula Writing Chapters 8 & 9 Honors Chemistry Ionic & Covalent Compounds

Chemical Bonds Atoms rarely exist alone When atoms are bonded together, they are more stable chemical bond – mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together OR the attraction between a positive ion and a negative ion

Ionic Bonds results from electrical attraction between cations and anions atoms donate or accept electrons from each other

Covalent Bonds results from sharing of electron pairs between two atoms the electrons shared belong to both atoms

Covalent vs. Ionic Bonding

Bonding Patterns What generally occurs with elements is if you have: metals + nonmetals = ionic compounds nonmetals + nonmetals = covalent compounds Of course there will be exceptions! We will discuss this more later.

Ionic Compounds Ionic bonds do NOT form molecules Chemical formulas for ionic compounds represent the simplest ratio of ion types Made of anions and cations Binary ionic compounds contain only two different types elements. Other ionic compounds contain polyatomic ions they will have more than two different types elements.

Formation of Ions Cations - formed when atoms lose electrons  Generally metals and hydrogen  All group 1 metals will lose one e- to become 1+ ions (Hydrogen follows this too when bonded to another non-metal)  All group 2 metals will lose two e- to become 2+ ions  Aluminum will lose three e- to become 3+ ion  Zinc will lose two e- to become 2+ ion  Silver will lose one e- to become 1+ ion

 The other metals you will need help to figure out how many e- they will lose because of the d-orbital e- they can lose 1, 2, 3, or even 4 electrons.  You can figure out what their charges are based on their names they will have roman numerals that indicate their charge. Ex: Lead(IV) ion means Lead ion with a 4+ charge

Anions - formed when atoms gain electrons  Generally nonmetals and sometimes hydrogen when it is bonded to metals  All group 15 nonmetals will gain 3 e- to become 3- ions  All group 16 nonmetals will gain 2 e- to become 2- ions  All group 17 nonmetals will gain 1 e- to become 1- ions (Hydrogen follows this too when bonded to metals) In order to tell when we are talking about an anion, we use the ending –ide on the root name of the element.  Examples: 1.Cl - becomes chloride 2.O 2- becomes _____________ 3.S 2- becomes _____________ 4.N 3- becomes _____________

Ionic Compounds Ions combine so that amount of positive and negative charge is equal Usually crystalline solid at room temp. Formula of ionic compound depends on the charges of the ions combined

Ionic Compounds Continued… The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s).

Naming Chemical Compounds: Ionic & Covalent

Classifying Compounds The system for naming an ionic compound is different from that for naming a covalent compound, so before a compound can be named, it must be classified as ionic or covalent. Classifying a compound is not an easy task, but for the purposes of naming them, we employ a simple test: If the answer is yes, use the system for naming ionic compounds. If the answer is no, use the system for naming covalent compounds. Is there a metal or a polyatomic ion present?

Naming Ionic Compounds Examples:  KI  MgCl 2  AgBr Answers:  Potassium iodide  Magnesium chloride  Silver bromide Most ionic compounds are named simply by naming the ions present.

There are, however, two complicating factors: Naming Ionic Compounds (continued) I. Some metals form more than one ion. II. Identifying polyatomic ions I. Metals that form more than one ion, such as iron, add a Roman numeral to the name to indicate the charge: Fe 2+ is called iron (II) and Fe 3+ is called iron (III) Assume a Roman numeral is required for any metal except 1. metals in groups 1 and 2 on the periodic table 2. aluminum (3+), silver (1+), and zinc (2+) always keep the same charge

Naming Ionic Compounds (continued) If a Roman numeral is required, the charge on the metal ion must be determined from the charge on the negative ion. Helpful Rules to Remember FormulaReasoningName FeCl 2 Cl has a 1- charge, and there are 2 of them for a total of 2-, so the Fe must be 2+ iron (II) chloride Fe 2 O 3 O has a 2- charge, and there are 3 of them for a total of 6-, so the Fe must have a total charge of 6+ split equally between the two iron atoms, so each must have a 3+ charge iron (III) oxide PbS 2 S has a 2- charge, and there are 2 of them for a total of 4-, so the Pb must be 4+ lead (IV) sulfide Cu 3 N N has a 3- charge, so the Cu must have a total charge of 3+ split equally between the 3 copper atoms, so each must have a 1+ charge copper (I) nitride Examples A metal ion is always positive. The Roman numeral indicates the charge, not the subscript. The positive and negative charges must cancel (total charge must = 0). Nonmetals are always negative & can never form more than one monatomic ion.

Naming Ionic Compounds (continued) II. Polyatomic ions each have specific names which must be memorized so they can be recognized on sight. (At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.) You will need to know these ions for quizzes and tests!

Naming Ionic Compounds Examples Na 2 SO 4 sodium sulfate Fe(NO 3 ) 2 iron (II) nitrate AlCl 3 aluminum chloride PbI 4 lead (IV) iodide (NH 4 ) 3 PO 4 ammonium phosphate Mg 3 N 2 magnesium nitride AgC 2 H 3 O 2 silver acetate

Naming Ionic Compounds Practice: Na 2 CO 3 sodium carbonate Ni 2 O nickel(I) oxide K 2 O potassium oxide Cu 3 PO 4 copper (I) phosphate CoI 3 cobalt (III) iodide AnalysisIf “Yes” * Is the cation a metal? (If so, does it need a Roman numeral? The compound is ionic: name each ion present (DO NOT USE PREFIXES) * Is there a polyatomic ion present? * Are both elements nonmetals? The compound is covalent: use prefixes (NO CHARGES EXIST) PbI 3 Lead(III) iodide metal present  ionic  no prefixes Na  group I  no Roman numeral metal present  ionic  no prefixes Ni  tranistion metal  use Roman numeral (O is 2-, each Ni must be 1+) metal present  ionic  no prefixes K  group I  no Roman numeral metal present  ionic  no prefixes Cu  not group I, II, etc.  add Roman numeral (PO 4 is 3-, each Cu must be 1+) metal present  ionic  no prefixes Co  not group I, II, etc.  add Roman numeral (I is 1-, total is 3-, Co must be 3+) metal present  ionic  no prefixes Pb  not group I, II, etc.  use Roman numeral (each I is 1-, so the Pb must be 3+) NH 4 Br ammonium bromide NH 4  polyatomic ion present  ionic  no prefixes

Writing Formulas for Ionic Compounds

Formulas for ionic compounds are written by balancing the positive and negative charges on the ions present. The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s). Polyatomic ion names must still be recognized from memory (e.g. ammonium nitrate), but metals will have a Roman numeral associated with them if there is the possibility of more than one ion (e.g. copper (I) chloride or copper (II) chloride). The Roman numeral indicates the charge on the ion not the number of ions in the formula.

Writing Formulas for Ionic Compounds (continued) Helpful Rules to Remember NameReasoningFormula ammonium sulfate NH 4 has a 1+ charge & SO 4 has a 2- charge, so 2 ammonium ions are required for each sulfate. (NH 4 ) 2 SO 4 zinc chloride Zn has a 2+ charge & Cl has a 1- charge, so 2 chloride ions are required for each zinc ion. ZnCl 2 copper (II) phosphate Cu has a 2+ charge & PO 4 has a 3- charge, so 3 copper (II) ions are required for every two phosphate ions. Cu 3 (PO 4 ) 2 Examples A metal ion is always positive. The Roman numeral indicates the charge, not the subscript. The positive and negative charges must cancel (total charge must = 0). If more than one polyatomic ion is needed, put it in parentheses, and place a subscript outside the parentheses.

Writing Ionic Compound Formulas sodium chloride iron(III) oxide magnesium hydroxide lithium carbonate NaCl Fe 2 O 3 Mg(OH) 2 Li 2 CO 3

Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names. The compounds named in this way are binary covalent compounds. ‘Binary’ means that only two atom are present. A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.) A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘-ide’.

Naming Covalent Compounds Prefixes Used SubscriptPrefix 1mono- 2di- 3tri- 4tetra- 5penta- SubscriptPrefix 6hexa- 7hepta- 8octa- 9nona- 10deca- Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Naming Binary Covalent Compounds: Examples N 2 S 4 dinitrogen tetrasulfide NI 3 nitrogen triiodide XeF 6 xenon hexafluoride CCl 4 carbon tetrachloride P 2 O 5 diphosphorus pentoxide SO 3 sulfur trioxide 1mono- 2di- 3tri- 4tetra- 5penta- 6hexa- 7hepta- 8octa- 9nona- 10deca- Second element in ‘-ide’ from * Drop –a & -o before ‘oxide’

Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number of atoms of each element present. Remember:  The compounds named in this way are binary covalent compounds (they contain only two elements, both of which are nonmetals).  When in covalent compounds, atoms do not have charges.  Subscripts are determined directly from the prefixes in the name. If no prefix is present on the name of the first element, there is only one atom of that element in the formula. A prefix will always be present on the name of the second element. The second element will use the form of its name ending in –ide.

Writing Formulas for Binary Covalent Compounds: Examples nitrogen dioxide NO 2 diphosphorus pentoxide P2O5P2O5 xenon tetrafluoride XeF 4 sulfur hexafluoride SF 6 1mono 2di 3tri 4tetra 5penta 6hexa 7hepta 8octa 9nona 10deca * Second element in ‘ide’ from * Drop –a & -o before ‘oxide’ dihydrogen monoxide H2OH2O

What about these???? Some elements and compounds look as though they should be named as covalent compounds but we don’t: ‘SUPER 7’  N 2, O 2, F 2, Cl 2, Br 2, I 2, and H 2  Diatomic elements  Named by using the elements name only

Commonly named compounds:  H 2 O = water  NH 3 = ammonia  CH 4 = methane Methane is an organic compound and they have completely different rules for naming

Common Acids There are only 5 Acids that you are Required to Know  HCl = hydrochloric acid  HNO 3 = nitric acid  H 2 SO 4 = sulfuric acid  H 2 CO 3 = carbonic acid  H 3 PO 4 = phosphoric acid

Writing Chemical Formulas: A Review I. Ionic Compounds II. Covalent Compounds

Classifying Compounds Using Names Classifying a compound using its name is not as difficult as using its formula. The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.). If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes, such as dichromate, but those will be memorized and recognized as ions.) If there is an H- in front the compound will usually be an acid.

Writing Formulas Practice: carbon tetrafluorideCF 4 Na 3 PO 4 sodium phosphate Cu 2 SO 4 copper(I) sulfate AnalysisIf “Yes” The compound is covalent: the prefixes give the subscripts. * Are there prefixes present? Is there a roman numeral or name of an ion? The compoun d is ionic: subscripts must be determine d by balancing charges prefixes  covalent  prefixes indicate subscripts metal  ionic  balance charges  3 Na 1+ needed for 1 PO 4 3- metal present  ionic  balance charges  2 Cu 1+ needed for 1 SO 4 2- Al 2 S 3 aluminum sulfide metal present  ionic  balance charges  2 Al 3+ needed for 3 S 2- N 2 O 5 dinitrogen pentoxide prefixes  covalent  prefixes indicate subscripts NH 4 NO 3 ammonium nitrate polyatomic ion present  ionic  balance charges  1 NH 4 1+ needed for 1 NO 3 1- PbO 2 lead(IV) oxide metal present  ionic  balance charges  1 Pb 4+ needed for 2 O 2- Fe 2 (CO 3 ) 3 iron(III) carbonate metal present  ionic  balance charges  2 Fe 3+ needed for 3 CO 3 2-